I love them both
I used them both in my teams and they are very fun to use. You will appreciate Froslass especially after she'll set up spikes while your opponent boosting itself only to get OHKOed with Destiny Bond .
A stalllbreaker is a Pokemon that can deal with stall. Stall is the definition for Pokemon that are not aimed to win you by offensive moves, but with moves that can wear you down while healing themselves such as Will-O-Wisp, Wish, Protect, Toxic, Thunder Wave Heal Bell etc. Usually these Pokemon are very bulky too, so offensive Pokemon cannot OHKO them. Clefable is actually a good stallbreaker. Magic Guard protect it from hazards, toxic and burns and Calm Mind boost it's Special attack so it can OHKO the bulkiest Pokemon before they can heal up. Since Clefable is your set up sweeper, it is recommended that you'll find another stallbreaker so you won't drop too much things for your Clefable to deal with. On the flip side, since Clefable is very good for switching in and out for Garchomp, maybe you want to use Clefable as your stallbreaker and think of another set up sweeper?
I think it's best because if you do that, then we can choose a faster set up sweeper that is better to keep for the end after Empoleon-Garchomp-Clefable core wears down your opponent.
Oh wait, I totally forgot about Weavile
Weavile is great for an end game cleaner. and you can use SD to potentially set up and do a massive damage to stall. Its speed and priority Ice Shard deals well with offense and he also has Knock Off which is great to remove items that can change the situation like Choice Scarf.
OK so we have:
1. Froslass/Mamoswine - Lead with SR/Spikes
2. Empoleon - Special wall and attacker.
3. Garchomp- Revenge Killer
4. Clefable - Stallbreaker
5. Weavile - End game cleaner, set up sweeper.
I would put in the final spot a Mega Pokemon of course because why not? :]